It is known that relatively intense compressional wave energy in a focused far field of an ultrasonic transducer array can be used for therapeutic purposes. The ultrasonic focused far field compressional wave energy produces hyperthermia effects to raise the temperature of treated malignant tissue sufficiently to destroy same. Typically, the array transducers are excited with frequencies in the 0.5-2 megahertz region.
In the past, the array transducers have typically been narrow bandwidth resonant devices, effective over only a narrow frequency band, e.g., 50 kilohertz. The transducers have been excited at a frequency that is approximately equal to the resonant frequency thereof to provide greatest efficiency between an electric energy source and the transducers. Hence, the treating transducers have generally been driven at a single frequency or frequencies in a very narrow band. The ultrasonic energy derived from the transducers is coupled directly by contact to the skin of the subject or is coupled indirectly to the subject by way of a compressional wave transmitting liquid, such as water.
Because of the single frequency or narrow band width excitation and the narrow band width characteristics of the prior art transducer arrays, single arrays formed of such transducers have not been well adapted to efficiently and effectively treat both shallow and deep regions, i.e., regions which are respectively close to and far from the surface of the skin of the subject where the focused far field hyperthermia compressional wave energy enters the subject. For the most efficient and effective treatment, the frequency of the compressional wave energy is inversely related to the depth of the treated region so that deep regions are treated with low frequency energy and vice versa for shallow regions. Narrow bandwidth arrays do not have adequate bandwidth to couple energy efficiently and effectively to deep and shallow regions.
The narrow bandwidth treating arrays are not particularly well adapted for both diagnostic and hyperthermia treating purposes. Most diagnostic ultrasonic compressional wave systems utilize echo techniques wherein an ultrasonic compressional wave energy pulse is derived from a transducer, transmitted to the subject and reflected from interior regions of the subject back to the same transducer which derived it. The travel time of the ultrasonic compressional wave pulse, from the time it leaves the transducer until the time the reflected energy is coupled back to the transducer, is a measure of the location of a region of interest in the body of the subject. Typically, the regions of interest are bones, air pockets in the subject, various body organs and malignant regions. The amplitude of the reflected energy incident on the transducer provides an indication of the nature of the reflecting region in the subject.
When a narrow bandwidth transducer, e.g., as employed in prior art hyperthermia devices, is supplied with a pulse of electric energy, the transducer typically "rings" in a manner similar to a shock excited resonant circuit to derive a sequence of damped sine wave like oscillations at the transducer natural frequency. If a typical prior art narrow band width transducer previously employed for hyperthermia treatment purposes were pulsed to enable a reflected pulse to be coupled back to it for diagnostic purposes, the transducer would still be ringing at the time the reflected energy is coupled back to the transducers. If a transducer is ringing when the reflected energy is coupled back to it, the transducer does not derive an accurate replica of the reflected energy wave incident thereon. Hence, little or no information can be derived for diagnostic purposes with the narrow bandwidth transducer arrays previously employed for hyperthermia treating purposes.
It is, accordingly, an object of the present invention to provide a new and improved apparatus for and method of utilizing ultrasonic compressional wave energy for hyperthermia treating and diagnostic purposes.
Another object of the invention is to provide a new and improved apparatus for and method of hyperthermia treating and analyzing a subject with ultrasonic compressional wave energy derived from the same transducers of an electric energy - compressional wave energy transducer array.
Another object of the present invention is to provide a new and improved apparatus for and method of treating deep and shallow regions of a subject with compressional wave energy derived from the same transducers of a compressional wave transducer array.
Presently developed ultrasonic compressional wave hyperthermia treating arrays emit continuous wave beams having relatively low power levels such that there is approximately a linear relationship between the heating effect at the focused far field treated area and the beam instantaneous power or intensity. A problem with such ultrasonic compressional wave hyperthermia treating arrays is that the subject, typically a human patient being treated for destruction of cancerous tumors, is subjected to considerable pain when a beam from an array transducer is incident on certain untreated areas. Typically the pain occurs because a bone is in a beam path from a particular transducer in the array. The irradiated bone is frequently remote from the region on which the far field is focused. However, it may be proximate the focused far field region. Because of the bone pain problem and the need to limit the maximum amount of energy that can be applied to a treated region where the far fields of several beams are focused, the power of the continuous hyperthermia compressional wave energy in each beam must be limited. To prevent pain, the power in beams incident on such bones must be smaller than the power in the remaining beams.
It is accordingly still another object of the invention to provide a new and improved compressional wave hyperthermia treating system and method using a far field focused transducer array that is activated so as to reduce the amount of pain that a subject experiences during treatment.
A still further object of the invention is to provide a new and improved compressional wave hyperthermia treating system and method using a far field focused transducer array that is activated so that the effective power level applied to a treated area is increased without exceeding the permissible energy level that can be safely applied to the treated region.